In order to accommodate variations in alignment between a drive and driven shaft, it has been the practice to locate a flexible coupling in the path to effect torque transmission. In some constructions, due to either torque magnitude requirements or other structural considerations, substantially more robust couplings are required that are capable of accommodating misalignment or vibration in use. For example, in some high torque load environments and/or high speed transmissions, a metal diaphragm flexible coupling assembly such as disclosed in U.S. Pat. No. 5,000,722 granted Mar. 19, 1991 and U.S. Pat. No. 5,588,917 granted Dec. 31, 1996 is employed.
In a number of torque transmission set ups, a bolted assembly such as is conventionally used with flexible coupling members cannot be employed due to a number of factors such as the types of shafts that require connection, the magnitude of the torque load or the rotational speeds to be imposed on the members or the environment in which the coupling is to be established. In other circumstances, the end user's requirements demand a more sturdy or durable assembly. With such conditions, the attachment of one or both connection elements of the flexible coupling necessitate more secure attachment of the flexible coupling to the drive and driven shafts such as a shrink fitting between the flexible coupling attachment members and the drive and driven shafts. The use of a shrink fitting of the attachment members of a flexible diaphragm type coupling, however, introduces a manufacturing difficulty since the magnitude of the dimensional variation that results from the shrink fitting is often difficult to predict with the required accuracy to assure long life and stable operation of many types of flexible couplings. This is particularly troublesome where the flexible elements of the coupling are metal diaphragms such as disclosed in the aforementioned patent. In other prior art arrangements where a flexible diaphragm is formed integrally about a connection hub or sleeve, the outer peripheral edge of the diaphragm is attached to a connection flange but with the diaphragm placed in one of two conditions. In one condition, the diaphragm is substantially flat or planar in a radial sense. While this condition imposes little or no stress on the diaphragm, the diaphragm has exhibited a tendency to pop or deflect suddenly due to any misalignment or vibration occurring. Such instability can lead to early failure of the coupling as well as damage to the coupled machinery.
In the other condition, the practice has been to deflect the diaphragm prior to placing the coupling in service and prior to shrink fitting the hub of the coupling to a shaft. In this arrangement, when the shrink fitting takes place, the predeflected diaphragm could further bend to absorb the radial expansion caused by the presence of a coupled shaft in the hub. However, it has been recognized that this pre-deflection condition frequently places the diaphragm under high stress caused also by the compression caused by shrink fitting of the hub to a shaft. That is to say, where the hub has been heated to allow insertion of a shaft end, the subsequent cooling of the hub in the presence of the shaft limits the shrinkage and can cause or add to the deflection in the diaphragm. This is undesirable in such applications as it often creates stresses throughout the diaphragm element in the assembled condition. Under some conditions, the flexible diaphragm will be deflected such that when vibrated in use, early failure of the coupling may result particularly under high torque loads. Attempts to minimize these conditions in such couplings require extensive testing of the coupling. This is time consuming and expensive for each such coupling for each application to determine the effect of the shrink fitting on the diaphragm or each of them where two are used in the coupling member.